1. Field of the Invention
This invention relates to electric motors and, in particular, to the rotatable attachment of a rotor to a stator in such a motor.
2. Description of Related Art
U.S. Pat. No. 5,247,216, which is hereby incorporated by reference, discloses an electric motor of one type with which the invention is useful. This motor, as is illustrated in the exploded view of FIG. 1, includes a number of component parts assembled along a central axis X--X. The parts include a shaft 22, a flange 24, a housing 26, a stator 28, a rotor 30, a ball bearing 32 rotatably mounted on one end of the rotor, an elastomer O-ring seal 34, and an electrical connector 36. In the assembled motor, as is illustrated in FIG. 2, the flange 24 serves to mount the motor such that an operative end 70b of the shaft 22 is positioned to perform a control function. The shaft itself includes a threaded cylindrical portion 66, which is rotatably engaged with an internal thread of rotor 30, and a non-circular (e.g. rectangular) shaped cross section portion 54. The stator 28 includes an opening 44 at a first end for closely holding the bearing 32, a central opening 46 for receiving a central magnetic portion of the rotor 30, and two openings 48 and 50 at a second end. Opening 50 has a non-circular shape, corresponding with that of the shaft portion 54, for slidably receiving portion 54 and translating rotational motion of the rotor into linear motion of the shaft. Opening 48 of the stator 28 receives a cylindrical end 52 of the rotor 30 and has an inner surface which cooperates with an outer surface of the end 52 to form a journal bearing.
Both the cylindrical end 52 of the rotor and the portion of the stator including the receiving opening 48 are injection molded out of plastic materials to precise tolerances to effect a close fit which is neither binding nor so loose as to allow vibration. This increases the manufacturing complexity of the motor, and particularly of the already complex-to-manufacture stator.